Grain oriented silicon steel, as an important magnetic material, has excellent high magnetic induction and low iron loss properties, and is widely used as a core material for power transformers. Insulation coating formed on a surface of the grain oriented silicon steel not only has the effects of rust prevention, corrosion resistance, and insulation, but also tension generated on the surface can reduce the iron loss, reduce magnetostriction coefficient, and reduce energy consumption and noise of the transformer. Therefore, the insulation coating is an important part of the grain oriented silicon steel.
However, most of insulation coating contains chromates. Hexavalent chromium is always present in the surface coating of the steel sheet after chromate-containing insulation coating is applied to the steel sheet to form a film after high-temperature drying and sintering. If discarded steel sheets are not properly recovered, it will endanger human health and also seriously pollute the environment. While if the hexavalent chromium in the coating is recovered, cost will be greatly increased. Therefore, it is an urgent requirement for the silicon steel industry in domestic and abroad to develop silicon steel insulation coatings that do not contain toxic hexavalent chromium in the coating final product and have excellent comprehensive properties, and are easy to recycle. As an alternative to chromic anhydride, JP 2000169973 discloses a method of adding a boron compound instead of a chromium compound. JP 2000169972 discloses a method of adding an oxide colloid. However, regardless of which of the above techniques is used, the overall performance of the coating cannot be achieved comparable to that of a chromium-containing coating.
Therefore, the prior art, in particular, the chromium-free insulation coating with good performance has yet to be improved and developed.